Aromatic urethane bonds are known to evanesce at elevated temperatures leaving behind aromatic alcohols and aromatic isocyanates. This phenomenon is used to form water-based urethane coatings that are stable at room temperature. Such coatings contain isocyanates which have been reacted with a material such as, for example, phenol, to create a reversible aromatic urethane bond. Isocyanates that have been blocked in this manner are unable to react at room temperature with compounds that normally react with isocyanates but will react at temperatures which cause the aromatic urethane bond to evanesce.
Nonwoven fibrous webs having strength and toughness are typically formed from high molecular weight polymers. Those polymers usually have low melt flow rates and are normally processed at temperatures near the polymer's degradation temperature to improve processability. The resulting fibers and webs may contain polymers that are partially degraded causing some loss of desired physical properties. In some situations, high molecular weight polymers may be partially degraded by overheating to increase the melt flow rate of the polymer to a useful range for processing.